Finally got two rooms all sanded and prepped for the polyurethane. I decided to use a water based rather than oil. How many gallons should I anticipate using on roughly 600-650 sq feet of floor? I'm expecting I'll use 3-4 coats.

I'm looking at using their Super Fast-Drying Polyurethane for Floors. which covers 600-700 sq feet per gallon.

Right now i have the floors down to bare wood. This weekend I'm going to rent a large orbital sander (the one with 3 pads) and go over it with the 60 and 80 grit before applying the poly. On the Minwax site they recommend applying a sanding sealer on the bare wood before applying the poly.

Does this bring out the grain and allow the poly to sink in better?
Should I apply the sealer before sanding this weekend?
Also will I need to sand between coats of the poly?

Any moisture will make loose fibers stand up so you can sand them off. Depending on the wood sometimes you can do this with a wet rag allow to dry and sand. You will still get more after your first coat. Between coats use one of those green dish scrubbers pads.

Thanks for the tips everyone. It went really smooth when i finished the floors. I also really suprised at how easy it was and how good they turned out. The can said 500-600sq feet per gallon, I finished about 500sq feet of flooring with 4 coats and only used a gallon and a half. One of the rooms is maple wood and the other is pine.

I did the first coat on a friday night, gave the finish about 16 hours before the second coat. I used one of those sanding blocks attached to a pole with 220 grit sand paper between the first and second coat and cleaned up the dust. Then did the 3 additional coats on that saturday with 2 hours between each coat. The floors look amazing! If anyone is scared to do their own floors; don't be. Just take your time and you'll be surprised with the results. Really the hardest part of the whole process was removing the old finish.